Retaining the structural strength of the cement itself does nothing about the fact that you've introduced a big lubricated slipface into the structure, namely t

Retaining the structural strength of the cement itself does nothing about the fact that you've introduced a big lubricated slipface into the structure, namely the membrane. Here's my best idea: You pour regular reinforced concrete in sort of a waffle pattern, make a bunch of capacitor cells in the holes, then put another layer of concrete on top. The individual membranes have limited shear stress. Leaks are isolated. Presumably cells of mostly concrete and water still have pretty good compressive strength, so maybe it will hold together like that. I'm guessing you at least have to increase the total slab thickness, though. I'm guessing there will be some kind of creative architecture like that before it goes to prod, anyway.